A child receives a tall beautiful plant as a birthday gift from his father with a quiz. The father asked her how she would verify whether this tall plant was the progeny of both the tall parents or one tall and one short parent plant. She could verify this through?
self-pollination
Verifying Plant Parentage Through Genetic Principles
The question describes a scenario where a child receives a tall plant and needs to determine if its parents were both tall or if one was tall and one was short. This requires understanding how traits like height are inherited in plants, specifically involving dominant and recessive alleles.
Understanding Dominant and Recessive Traits
Let's assume that the tall trait is dominant and the short trait is recessive. We can represent the allele for tallness with 'T' and the allele for shortness with 't'.
- A plant with genotype TT will be tall (homozygous dominant).
- A plant with genotype Tt will be tall (heterozygous).
- A plant with genotype tt will be short (homozygous recessive).
The tall plant received by the child could have the genotype TT or Tt, as both result in a tall phenotype. The parentage question implies knowing if the plant inherited at least one recessive allele ('t') from a parent. If the plant is Tt, it must have received a 't' allele from one parent. If it is TT, it received 'T' alleles from both parents.
Evaluating the Verification Methods
Let's analyze the given options to see how they could help determine the genotype of the tall plant and thus infer its parentage.
| Option | Explanation | Usefulness for Verification |
|---|---|---|
| Cross-pollination | Mating the tall plant with another plant. The outcome depends entirely on the genotype of the plant it is crossed with. If crossed with a dominant plant (TT or Tt), it might not reveal the tall plant's genotype. A test cross (crossing with a homozygous recessive 'tt' plant) is a specific type of cross-pollination used for verification, but "cross-pollination" alone is too broad. | Potentially useful, but lacks specificity without knowing the cross partner. A specific cross (test cross) is required. |
| Self-pollination | Allowing the tall plant to pollinate itself. This is possible for plants that have both male and female parts or where pollen from one flower can fertilize ovules of the same flower or another flower on the same plant. | Highly useful. The progeny ratio from self-pollination reveals the genotype of the parent plant. |
| Tissue culture | A method of propagating plants from small tissue pieces in a sterile lab environment. This produces clones (genetically identical copies) of the parent plant. | Not useful for determining the original parentage based on genetic inheritance patterns. It creates identical copies, it doesn't reveal the genotype regarding heterozygosity for a recessive trait. |
| Negative propagation | This is not a standard biological term related to plant genetics or propagation methods used for determining genotype or parentage in this context. | Not a valid method for this purpose. |
Verification by Self-Pollination
Self-pollination is the key method here. Consider the two possible genotypes of the tall plant:
-
Case 1: The tall plant is homozygous dominant (TT).
If the plant's genotype is TT, self-pollination (TT x TT) will result in offspring with genotype TT.
All progeny will be tall. \([ \\)text{Parents: TT} \(times \\)text{TT} \(] \\)[ \(text{Gametes: T, T} \\)times \(text{T, T} \\)] \([ \\)text{Offspring: TT} \(text{ (all tall)} \\)] -
Case 2: The tall plant is heterozygous (Tt).
If the plant's genotype is Tt, self-pollination (Tt x Tt) will result in offspring with a mix of genotypes: TT, Tt, and tt.
Specifically, the genotypes will be in the ratio 1:2:1 (TT:Tt:tt), and the phenotypes will be in the ratio 3:1 (Tall:Short). \([ \\)text{Parents: Tt} \(times \\)text{Tt} \(] \\)[ \(text{Gametes: T, t} \\)times \(text{T, t} \\)] \([ \\)text{Offspring Genotypes: TT, Tt, Tt, tt} \(] \\)[ \(text{Genotype Ratio: 1 TT : 2 Tt : 1 tt} \\)] \([ \\)text{Phenotype Ratio: 3 Tall : 1 Short} \] The presence of even a single short (tt) offspring confirms that the tall parent plant must have been heterozygous (Tt).
If the tall plant produces any short offspring after self-pollination, it must be heterozygous (Tt). A heterozygous tall plant (Tt) could have resulted from one tall parent (TT or Tt) and one short parent (tt), or from two heterozygous tall parents (Tt x Tt). However, if the plant produces *only* tall offspring after self-pollination over several generations, it is likely homozygous dominant (TT), which could result from two tall parents (TT x TT, TT x Tt, or Tt x Tt, provided no tt offspring were selected).
Therefore, self-pollination is the method that directly reveals whether the tall plant carries the recessive allele 't'. If it carries 't' (i.e., is Tt), it implies a parent contributed this allele, which could easily be a short parent (tt).
Conclusion on Verification Method
Allowing the tall plant to self-pollinate and observing the characteristics of its offspring is the standard method to determine if it carries the recessive allele for shortness. If short offspring appear, the plant was heterozygous (Tt), indicating one of its parents likely contributed the 't' allele. If only tall offspring appear over sufficient number of progeny, the plant is likely homozygous dominant (TT).
Revision Table: Plant Genetics Key Terms
| Term | Definition | Example |
|---|---|---|
| Allele | A variant form of a gene. | T (tall allele), t (short allele) |
| Genotype | The genetic makeup of an organism (combination of alleles). | TT, Tt, tt |
| Phenotype | The observable physical or biochemical characteristics of an organism. | Tall, Short |
| Dominant Allele | An allele that expresses its phenotype even when paired with a recessive allele. | T (tall) |
| Recessive Allele | An allele that expresses its phenotype only when paired with another identical recessive allele. | t (short) |
| Homozygous | Having two identical alleles for a trait. | TT, tt |
| Heterozygous | Having two different alleles for a trait. | Tt |
| Self-pollination | Pollination of a flower by pollen from the same flower or another flower on the same plant. | A pea plant's pollen fertilizing its own ovules. |
| Cross-pollination | Pollination of a flower by pollen from a flower on a different plant of the same species. | Pollen from a tall plant fertilizing a short plant. |
| Test Cross | Crossing an organism with a dominant phenotype but unknown genotype with a homozygous recessive organism. | Crossing a tall plant (TT or Tt) with a short plant (tt). |
Additional Information: Test Cross vs. Self-Pollination
While self-pollination works for plants capable of it, a test cross is a general method applicable to any organism where a homozygous recessive individual is available. In a test cross, the organism with the dominant phenotype (unknown genotype TT or Tt) is crossed with a homozygous recessive organism (tt). The progeny reveal the genotype:
- If the dominant parent was TT, the cross TT x tt produces all Tt offspring, which are all tall.
- If the dominant parent was Tt, the cross Tt x tt produces Tt and tt offspring in a 1:1 ratio. This means half the offspring will be tall and half will be short.
Both self-pollination (for self-compatible plants) and a test cross are powerful tools in genetics to determine the genotype of an individual showing a dominant trait.
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